Thermostat



June 23, 1931. w O, SNELLING 1,811,442

- 4 THERMOSTAT Filed Nov. 3, -1925 y Mn @if E l148'.jl J0 16 gia je i N .53 @L D 3l 32 34 4. t? if 6 2 8a n'ventox.'

Patented June 23, 1931 WALTER O. SNELLING, OF ALLEN'TOWN, :PENNSYLVANTA THERMOSTAT `Applioatflon med November This invention relates toy thermostats in general and more particularly to thermostats which act with a snap such for example as those used in connection with electrical devices where it is desired to avoid arcing during the making and breaking of the circuits.

The principal object of the present invention lies in the provision of an effective snap switch of simple construction. Aurther object lies in the provision of a bimetallic thermostat in combination with a resistant element which prevents the bimetallic bar from moving its free end under the influence of slight changes in temperature, but which 15, resistance will yield ata predetermined application o vforce allowing the thermostat barto snap forward upon reaching a chosen temperature. j

A still further object of the present invention' concerns improvements upon thermostat plates of the dented type, ysuch for example `as illustrated in Spencer Patent #1,448,240, March v13, 1923, vin that provision is made for altering at will the temperature at which the thermostat element will snap to circuit opening position as the iron becomes heated j to a high temperature. L

Figure 1 is a diagrammatic view of a lsimple form of the invention.

Figure 2 illustrates a 'modification in `which the thermostat moves a lever.

- Figure 3 shows a further modification, particularly applicable to a household iron.

Figure 4 shows a modification of the invention in .which the bar is not bi-metallic. Y Experiments have shown that if we notch the free end of a straight, bimetallic bar of the usual construction wherein the twoy members have different rates of ex ansion tension member into the-notch, the bar will distort until the accumulated tension is suiiiciently great to overcomevthe resistance offered by the holding of the .free end o f the bar' and will then snap tothe position to which it would have moved had there been no resistance to free movement.

' In such a structure avery simple manner of controlling the tension is by Ia spring with one end adjustable and the other end under heat and t a rounded ad]ustable 3, 1925. Serial No. 66,674.

engaging the rounded member. Such a spring can be made to hold the free end of the thermostat to any temperature ordinarily desired, and then when the critical point is reached and the accumulated tension overcomes the spring resistance Ithe thermostat will move with a snap, dispensing in such action all of the accumulated tension, and making the firm, quick contact so highly desired in connection with an elecf tricalA switch.

The invention may be applied to a great number of different devices, not onlyto electric switches but to anymechanical means wherein 'the thermostat vmoves a series of mechanisms. By offering resistance to the movement of the free end of the thermostat, whether a straight' bar, a loop, a coil, or even a compound thermostat, the range of temperature is greatlyincreased if the ofering of resistance in one direction is allowed to cause resistance in the opposite direction. In some cases this increased range is not desirable, and for these situations the resistance is so designed that itoffers a high resistance in one direction but a slight or negligible resistance in the opposite direction, this being. particularly desirable in an electric iron, where an .increase in range)l would be objectionable.

It is evident thatthe thermostat may control a valve, trigger, or switch of any kind and may also include signal mechanism indicating that made throughthe thermostat. Such indieating means are not shown in any ofthe drawings as they are-old and of well-known construction and not -per se a part of the invention. f

"In Figure 1, an extremely simple form of thermostat is shown consisting of a bimetallic element 10 of bar construction, anchored at one end as by the screw 11 to a permanent support 12. vThe free end of the compound bar is lprovided with a rounded nose 14 and may have near the end a Contact point 15 adapted to engage a ixed'contact' point 16 connected b Y the wire 17 to an electric circuit the returnefrom which is illustrated as a wire 18 here shown as connected to the certain changes have been Vdie as i fastenin means 11. The support 20, which is at a xed distance from the support 12, is threaded to receive an adjusting screw 21 which forms one abutment for a spring 2,2, which loosely surrounds the tension head 23 Which is provided with an optional handle 24E. A collar 26 forms the second abutment for the spring and a small added to limit the expansion ot the spring, particularly to prevent the tension head 23 from blocking movement of the nose 14. Adjustment of the strength of the spring 22 is controlled by the lrnurled head 28 of the threaded sleeve or screw 21.

The operation of this simple form is practically obvious. The bimetallic bar `upon an increase of temperature would Warp laterally by reason of the linear expansion of 'the metal having a higher coeiicient if there Were no resistance element. Longitudinal expansion is restrained by the other metal, usually steel, and the consequent movement therefore tends to move the har into arc shape, tangent at the point oit support. At the commencement of the movement, hovvever, 'the nose 1d engages the tension head and since the two ends of the thermostat,

har are held, it tends to distort, and this distortion 'With its consequent accumulation of energy increases until the stored torce is suhicient to overcome the strength of' the spring 22, at which time the nose rides over the `tension head forcing it into the sleeve 21. As soon as the point of the nose has passed the tension head, the spring 22 aids in the further movement of the thermostat and the contact of the electrodes 15 and 16 is consequently asnap engagement with no chance for arcing.` ln cooling the condition is very much the same, the har distorts, but the contact between and 16 is maintained until the spring 22 is overcome-'and the breakage of the current is also performed With a quick sudden snap. The nearer the sleeve 21 is moved toward thesupport 12, the greater the resistance offered the nose 14 and consequently vthe greater the temperature difference between od and on positions 1n Figure 2, the thermostat 30 is of the horse shoe type, one end being anchored as at 31 While the othenend-is pivoted as at 32 to ay link 33 having a substantially reci rof eating movement and here' illustrated as pivoted at its free end as at 34 to a lever 35 which lo turning about its pivot at the midustrated may control any sort oi mechanism or the lever itself may be the operating member of aquiclr acting electric snap switch. A

The resistance element in this invention is a straight leaf spring 36 anchored asat 37 to a support 38 at' a fixed distance from the 'thermostat anchor 31. A rod 39 having a handle 40 slips loosel through the support 38 and may be secure into adjustedposition guard 27 may be thereto by means of a set screw 41. The end of the rod'39 is bent laterally and is perforated, to receive freel the spring 36. By moving the lateral ben 43 of the rod 39 to- Ward the link 33, the free length of the spring is shortened and its resistance therey increased. 1n this modilication with increased temperature the bimetallic thermostat element 30 tends to separate its ends 31 and 32 and this is resisted by the spring 36 until the latter is hent out ot the Way at Which time the accumulated energyin the thermostat snaps the link 33 iforvvard to the right as shown in the ligure, giving a very powerful hlovv to the lovver pivoted end of the lever 35. Upon cooling, the small central depending lug 33a on the linlr 33 presses against the right hand side of spring 36 and i'inally snaps into position, this leaving the parts as shovvn in this ligure.

ln Figure 3 the free end of the temperature responsive element engages a rib or projection .in the spring 51 anchored vvith respect to the iron body, as isthe'thermostat element 52. A screw 5d having a threaded engagement with respect to the iron body may be adjusted at Will, by the knurled head 55 projecting Within easy reach of the operator. By turning the head 55, a greater or less resistance can be made to the movement of the free end of the thermostat plate 52 vvith a consequent increase in temperature range if the tvvo sides of thev cusp or bend in the spring are the same. It is desired, however, that the minimum temperature, i. e., that at Which the circuit is again closed, shall not be lowered and consequently it is preferred that the spring shall be as shown in the ligure, that is the rib or bend shall not be symmetrical but shall have a gentle slope 58, and an almost horizontal portion 59 which forms a shoulder or seat. With such a spring a heavy resistance is ollered to the movement of the thermostat to break the circuit and a very slight or almost negligible resistance is offered to movement of the thermostat plate to close the circuit, thus minimizing the increase in range by keeping the lower temperature constant. By such means the operator may keep a lovs7 maximum temperature When ironing handkerchiefs and by a mere turning of the lrnurled head 55 may obtain a high maximum temperature when later ironing thick garments.

ln Figure 4 the bar 60 is anchored at one end to the support l2 but the other end is Vnot free to bend laterally at the end being tted'loosely thru a guide 61 fixed with respect to the supports 12 and 20a. The spring 22 engages the end of the bar 60 and the top of the screw 21a so the resistance or pressure can be regulated as in the other forms. In this modication the longitudinal e-ilrpansion of the bar compresses the sponsive member, and means for altering at strong spring 22a and at al definite point the will the spring tension, said' means suri bar suddenly bends centrally, and the force rounding and guiding the in.

lstoredrin the spring isexerted to snap 4the center electrode lwdinto contact making position. It is obvious that the Contactin surface having the two different angles to t e line of movement may be on either the adjustable member as shown in Figure 3 or on the temperature responsive member as -shown in Figure 1. Y

What I claim is;- d

1. In a thermostat, a bimetallic temperature responsive member anchored at one end,

yielding mealspressing against the member ing at will the spring tension, and manual means for withdrawing the pin from con-,H

and oering. resistance-to movement of the free end of said member in onelateral direction and offering less resistance to movement` of said free end in the opposite direction. 2. The device of claim 1 in whichthe pressure of the yielding means is adjusts able. L

3. In a thermostat, a temperature responsive member, a spring pressed pin yieldingly holding the temperature responsive member cfrom normal movement, the cooperatin surfaces of the pin and member belng s uc that the holdin force is greater against one direction o normal movement than against the other,/and means for altering at will the springtension. i

4. In a thermostat, atemperature res onsive member, a spring pressed pin yiel ingly holding the temperature responsive member from normal movement, means for altertact with the temperature responsive member.

5. In a thermostat, a temperature respon- K sive element anchored at one end, spring means opposing movement ofthe free endof said element, the spring means being so shaped as to offer greater opposing force tofmovement of the said endin one direction than-inthe other, means for adjusting the resistanceoffered by.' said spring means, amemberfcarried by said element and a second memberl fixed with respect to the anchored end so as to lie in the path of said member, one of said members being resilient.

6. In a thermostat, a tempera-ture responsive member, a spring pressed pin substan- Y tially parallel to said member, and yieldingly holding'said member from normal movement, and means for .altering at will the sprin tension. y

n a thermostat, a temperature res onslve member, a spring pressed pin -yiel i ly holding the temperature responsive member from normal movement, a projecting end on said pin for manually withdrawing it from contact with the temperature re- In testimony whereof I a my signature.

' WALTER O. SNELLING. 

